A superabsorbent polymer is a crosslinked partially neutralized polymer that is capable of absorbing large amounts of aqueous liquids and body fluids, such as urine or blood, with swelling and the formation of hydrogels, and of retaining the fluids under a certain pressure. Superabsorbent polymer compositions may include post-treatment of the superabsorbent polymer such as surface crosslinking, surface treatment, and other treatment. Superabsorbent polymer particles are particles of superabsorbent polymers or superabsorbent polymer compositions. Unless otherwise specified, the acronym “SAP” may be used herein in place of superabsorbent polymer, superabsorbent polymer composition, and particles thereof.
Commercially available superabsorbent polymer compositions typically include crosslinked polyacrylic acids or crosslinked starch-acrylic acid graft polymers, in which some of the carboxyl groups are neutralized with sodium hydroxide solution or potassium hydroxide solution. A primary use of superabsorbent polymer compositions is in absorbent composites that are used in absorbent articles, such as diapers, training pants, incontinence products, or feminine care products. For fit, comfort and aesthetic reasons, and from environmental aspects, there is an increasing trend to make absorbent articles smaller and thinner. This is often accomplished by reducing the content of high volume fluff fiber typically present in these articles. To ensure a constant total retention capacity of body fluids in the sanitary articles, the superabsorbent polymer composition content of the absorbent articles is typically increased.
Fluid distribution in an absorbent composite is generally dependent on: the amount of free liquid available for distribution, the structure and materials of the absorbent composite, and a time factor. However, current absorbent composites useful in absorbent cores of absorbent articles generally have inadequate (or less than desirable) fluid distribution properties. Poor fluid distribution decreases the full utility efficiency of absorbent composites as not all of the superabsorbent polymer composition absorbs the liquid (i.e., the SAP is not fully utilized).
One potential solution known in the art for improving fluid distribution in an absorbent composite is to use superabsorbent polymer compositions having a slow absorbency rate. The theory for using slow absorbency superabsorbent polymer compositions is that there would be diminished or delayed gel blocking and thereby would provide more free liquid, as well as more time for the liquid to distribute away from the insult target zone. However, although distribution may be enhanced using the slow superabsorbent, the absorbent composite typically does not provide necessary leakage protection.
As can be observed in the use of slow absorbency superabsorbent polymer compositions, there is a conflict between the functions of lockup and distribution. One problem is that the time required to lockup liquid into the superabsorbent polymer composition and open-up composite structure by SAP swelling is relatively long. It is the free liquid which is in the target zone during a fluid insult period which is difficult to get into the absorbent product core and is believed to be responsible for leakage of liquid from an absorbent product while in use. To reduce leakage, the superabsorbent material needs to lockup liquid at a rate similar to the liquid delivery rate so that an absorbent product has adequate fluid handling functionality. However, if the superabsorbent polymer composition absorbs the liquid, then distribution of liquid is reduced since there is no free liquid to be distributed after fluid insult.
There is a need for an absorbent composite or an absorbent system that demonstrates the ability for a SAP to quickly lockup liquid and then gradually release this liquid so that it may be distributed to result in desirable leakage and distribution behavior. There is a further need for an absorbent article which exhibits enhanced fluid distribution properties while maintaining enhanced lockup properties, thereby maximizing the absorbing capabilities of the absorbent article and/or its components thereof.